1. Field of the Invention
The present invention relates to a projector for projecting and displaying a display image formed by a reflection-type modulation device, such as a reflection-type liquid crystal device, on a projection plane.
2. Description of Related Art
Nowadays, a projector using a transmissive liquid crystal device as a light valve is well known as a method for displaying a large screen image. As an example of such a projector, a typical construction of a projector using three transmissive liquid crystal devices is shown in FIG. 12.
A light source 110 is composed of a light source lamp 111 and a paraboloidal reflector 112, and light emitted from the light source lamp 111 is reflected by the paraboloidal reflector 112 to enter a dichroic mirror 401. The light is separated into red light, green light, and blue light by two dichroic mirrors 401 and 402, each having wavelength-selectivity, and then illuminates transmissive liquid crystal devices 301R, 301G, and 301B corresponding to each color light. The light transmitted by each of the transmissive liquid crystal devices is synthesized by a cross-dichroic prism 420, and is projected and displayed on a projection plane 600 via a projection optical system 500. Reflecting mirrors 403, 404, and 405 for reflecting light beams are provided on an optical path of the red light and an optical path of the blue light.
In the cross-dichroic prism 420 used as a color-light-synthesizing unit, dichroic films are arranged in the form of an X. The color-light-synthesizing unit of the projector using three liquid crystal devices can be realized by arranging two cross-dichroic mirrors in parallel with each other instead of the cross-dichroic prism 420. The use of the cross-dichroic prism 420, however, is characterized by providing a bright projected image without using a large-aperture projection lens because the distance between the liquid crystal devices 301R, 301G, and 301B and the projection optical system 500 can be shortened as compared with a case where the two dichroic mirrors are arranged in parallel with each other.
In the conventional projector, however, while the optical path can be shortened by the use of the cross-dichroic prism 420 in a color-light-synchronization portion, the length of the optical path is considerably long in a color-light-separation portion because the dichroic mirrors 401 and 402, and the reflecting mirrors 403, 404, and 405 are used. Therefore, in the conventional projector, the light loss in a light separating process is large, and characteristics of the cross-dichroic prism 420 cannot be sufficiently utilized.
A light beam emitted from the light source 110 composed of the light source lamp 111 and the paraboloidal reflector 112 has a non-uniform light intensity distribution in a cross section of the light beam, and has characteristics such that the light intensity of illumination light near an optical axis of the light source is high, and the light intensity of the illumination light decreases with distance from the optical axis. Therefore, in the conventional projector shown in FIG. 12, the light intensity of the illumination light is non-uniformly distributed on the liquid crystal devices 301R, 301G, and 301B, which are areas to be illuminated, and non-uniform brightness or color shading occurs in an image projected on the projection plane 600.
Furthermore, when the brightness of the projected image is to be considerably increased using a light source lamp having extremely high optical output, light absorption is large in the liquid crystal devices of the conventional projector using the transmissive liquid crystal devices, and a large-scale cooling device for cooling the liquid crystal devices is absolutely required.
It is an object of the present invention to provide a projector capable of obtaining a bright projected image without using a large-aperture projection lens by shortening the length of an optical path to prevent the loss of light.
In addition, it is an object to provide a projector which reduces non-uniformity of light intensity distribution of illumination light in an area to be illuminated, and which provides uniform brightness and excellent image quality.
Furthermore, it is an object to provide a projector which does not require a large-scale cooling device even if a light source lamp having extremely high optical output is used.
A first projector of the present invention may consist of a light source, a first optical element for condensing a light beam from the light source and dividing the light beam into a plurality of intermediate light beams, a second optical element placed on the light-emitting side of the first optical element for converting the plurality of intermediate light beams into one type of polarized light beams and superimposing the polarized light beams on a reflection-type modulation device, only one reflection-type modulation device for modulating light emitted from the second optical element, a polarized light beam selection element placed on an optical path between the second optical element and the reflection-type modulation device for reflecting or transmitting the light emitted from the second optical element to allow the light to reach the reflection-type modulation device and for transmitting or reflecting the light modulated by the reflection-type modulation device to allow the light to reach a projection optical system, and a collimating lens placed between the second optical element and the polarized light beam selection element.
According to the above construction of the first projector of the present invention, the length of the optical path can be extremely shortened, and the loss of light can be minimized. Therefore, it is possible to obtain an extremely bright projected image without using a large-aperture projection lens.
As the first optical element, a lens array having, for example, a plurality of light beam-dividing lenses arranged in a matrix may be used. By dividing the light beam from the light source into a plurality of intermediate light beams with such a lens array, and by superimposing the intermediate light beams on an area to be illuminated, non-uniform luminance can be further reduced than that of a single light beam. Therefore, even if the light beam emitted from the light source has a non-uniform light intensity distribution within a cross section of the light beam, illumination light having uniform brightness can be obtained. In particular, when the light intensity distribution of the light beam is not random, but the light intensity distribution has a fixed tendency as seen in a light beam emitted from a light source composed of a light source lamp and a paraboloidal reflector, the use of the above first optical element can make the light intensity distribution and angular distribution of the illumination light on the area to be illuminated extremely uniform.
The second optical element separates each of the intermediate light beams into a p-polarized light beam and an s-polarized light beam, aligns the polarization direction, and finally superimposes the light beams on a single area to be illuminated. In the conventional projector, only one of the p-polarized light beam and the s-polarized light beam can be used and the light loss is large in some polarized light beams. If the second optical element of the present invention is used, however, both of the polarized light beams can be used most efficiently. Therefore, it is possible to obtain a bright image. Since the plurality of divided intermediate light beams are finally superimposed on the single area to be illuminated, the polarized light beams having uniform brightness can be obtained as illumination light even if the light beam emitted from the light source has a non-uniform light intensity distribution within the cross section of the light beam. In particular, even if the intermediate light beams cannot be separated into the p-polarized light beams and the s-polarized light beams with uniform light intensity distribution or spectral characteristics, or even if the light intensity or the spectral characteristics of one of the p-polarized light beams is changed in a process of making the polarization directions of both of the polarized light beams uniform, polarized light beams having uniform brightness and less color shading can be obtained as illumination light.
A second projector of the present invention may consist of a light source, a first optical element for condensing a light beam from the light source and dividing the light beam into a plurality of intermediate light beam, a second optical element placed on the light-emitting side of the first optical element for converting the plurality of intermediate light beam into one type of polarized light beams and for superimposing the polarized light beams on a reflection-type modulation device, an optical color-light-producing system for producing a plurality of color light by time division from light emitted from the second optical element, only one reflection-type modulation device for modulating color light produced by the optical color-light-producing system, a polarized light beam selection element placed on an optical path between the second optical element and the reflection-type modulation device for reflecting or transmitting the light emitted from the second optical element to allow the light to reach the reflection-type modulation device and for transmitting or reflecting light modulated by the reflection-type modulation device to allow the light to reach a projection optical system, and a collimating lens placed between the second optical element and the polarized light beam selection element.
It is possible to obtain advantages similar to those of the first projector by the second projector of the present invention. Furthermore, since a color image can be displayed without containing a color filter of large light loss in the reflection-type modulation device, it is possible to prevent the light loss and obtain a bright projected image.
A third projector of the present invention may consist of a light source, a first optical element for condensing a light beam from the light source and dividing the light beam into a plurality of intermediate light beams, a second optical element placed on the light-emitting side of the first optical element for converting the plurality of intermediate light beams into one type of polarized light beams and for superimposing the polarized light beams on a reflection-type modulation device, three reflection-type modulation devices for modulating color light of three colors, an optical color-light-separating-and-synthesizing system for separating a light beam emitted from the second optical element into color light of three colors and for synthesizing each color light modulated by the three reflection-type modulation devices, a polarized light beam selection element placed on an optical path between the second optical element and the optical color-light-separating-and-synthesizing system for reflecting or transmitting the light emitted from the second optical element to allow the light to reach the optical color-light-separating-and-synthesizing system and for transmitting or reflecting the light synthesized by the optical color-light-separating-and-synthesizing system to allow the light to reach a projection optical system, and a collimating lens placed between the second optical element and the polarized light beam selection element.
In the second projector of the present invention, since the function of separating light and the function of synthesizing light are achieved by the same unit, the necessity for placing dichroic mirrors 401 and 402, or reflecting mirrors 403, 404, and 405, as in the above-described conventional projector, is eliminated. Therefore, the length of the optical path can be extremely shortened, and the loss of light can be minimized. Therefore, an extremely bright projected image can be obtained without using a large-aperture projection lens.
As the first optical element, a lens array having, for example, a plurality of light beam-dividing lenses arranged in a matrix may be used. By dividing the light beam from the light source into a plurality of intermediate light beams with such a lens array, and by superimposing the intermediate light beams on an area to be illuminated, non-uniform luminance can be further reduced than that of a single light beam. Therefore, even if the light beam emitted from the light source has a non-uniform light intensity distribution within a cross section of the light beam, illumination light having uniform brightness can be obtained. In particular, when the light intensity distribution of the light beam is not random, but the light intensity distribution has a fixed tendency as seen in a light beam emitted from a light source composed of a light source lamp and a paraboloidal reflector, the use of the above first optical element can make the light intensity distribution and angular distribution of the illumination light on the area to be illuminated extremely uniform.
The second optical element separates each of the intermediate light beams into a p-polarized light beam and an s-polarized light beam, aligns the polarization direction of one of the polarized light beams with that of the other one of polarized light beams, and finally superimposes the light beams on a single area to be illuminated. In the conventional projector, only one of the p-polarized light beams and the s-polarized light beams can be used, and the light loss is large in some polarized light beams. If the second optical element of the present invention is used, however, both of the polarized light beams can be used most efficiently. Therefore, it is possible to obtain a bright image. Since the plurality of divided intermediate light beams are finally superimposed on the single area to be illuminated, the polarized light beams having uniform brightness can be obtained as illumination light even if the light beam emitted from the light source has a non-uniform light intensity distribution within the cross section of the light beam. In particular, even if the intermediate light beams cannot be separated into the p-polarized light beams and the s-polarized light beams with uniform light intensity distribution or spectral characteristics, or even if the light intensity or the spectral characteristics of one of the p-polarized light beams is changed in a process of aligning the polarization directions of both of the polarized light beams, polarized light beams having uniform brightness and less color shading can be obtained as illumination light.
In the third projector, one of constructions including two dichroic prisms, including one cross-dichroic prism, and including a wedge-like prism can be used as the color-light-separating-and-synthesizing optical system.
A fourth projector of the present invention may consist of a light source, a first optical element for condensing a light beam from the light source and dividing the light beam into a plurality of intermediate light beams, a second optical element placed on the light-emitting side of the first optical element for converting the plurality of intermediate light beams into one type of polarized light beams and for superimposing the polarized light beams on a reflection-type modulation device, an optical color-light-separating system for separating a light beam emitted from the second optical element into color light of three colors, three modulation devices for modulating each of the color light separated by the optical color-light-separating system, an optical color-light-synthesizing system for synthesizing the color light modulated by the three modulation devices, three polarized light beam selection elements placed on an optical path between the optical color-light-separating system and the optical color-light-synthesizing system for reflecting or transmitting the light emitted from the optical color-light-separating system to allow the light to reach each of the modulation devices, and for transmitting or reflecting the light modulated by the modulation devices to allow the light to reach the optical color-light-synthesizing system, and three collimating lenses, each placed between the optical color light-separating system and the polarized light beam selection element.
As the first optical element, a lens array having, for example, a plurality of light beam-dividing lenses arranged in a matrix may be used. By dividing the light beam from the light source into a plurality of intermediate light beams with such a lens array, and by superimposing the intermediate light beams on an area to be illuminated, non-uniform luminance can be further reduced than that of a single light beam. Therefore, even if the light beam emitted from the light source has a non-uniform light intensity distribution within a cross section of the light beam, illumination light having uniform brightness can be obtained. In particular, when the light intensity distribution of the light beam is not random, but the light intensity distribution has a fixed tendency as seen in a light beam emitted from a light source composed of a light source lamp and a paraboloidal reflector, the use of the above first optical element can make the light intensity distribution and angular distribution of the illumination light on the area to be illuminated extremely uniform.
The second optical element separates each of the intermediate light beams into a p-polarized light beam and an s-polarized light beam, aligns the polarization direction of one of the polarized light beams with that of the other one of polarized light beams, and finally superimposes the light beams on a single area to be illuminated. In the conventional projector, only one of the p-polarized light beam and the s-polarized light beam can be used and the light loss is large in some polarized light beams. If the second optical element of the present invention is used, however, both of the polarized light beams can be used most efficiently. Therefore, it is possible to obtain a bright image. Since the plurality of divided intermediate light beams are finally superimposed on the single area to be illuminated, the polarized light beams having uniform brightness can be obtained as illumination light even if the light beam emitted from the light source has a non-uniform light intensity distribution within the cross section of the light beam. In particular, even if the intermediate light beams cannot be separated into the p-polarized light beams and the s-polarized light beams with uniform light intensity distribution or spectral characteristics, or even if the light intensity or the spectral characteristics of one of the p-polarized light beams is changed in a process of aligning the polarization directions of both of the polarized light beams, polarized light beams having uniform brightness and less color shading can be obtained as illumination light.
In the fourth projector, since the three polarized light beam selection elements corresponding to each of color light are used, the wavelength range of the polarized light beam selection elements can be restricted, and both an increase in performance and a cost reduction can be relatively easily achieved. Therefore, it is possible to realize a brighter projected image having a wider range of colors.
As a polarized light conversion element of the second optical element in the above first to fourth projectors, a plate-like polarized light conversion element can be employed which includes a polarized light separation unit array in which a plurality of polarized light separation units each having a pair of a separation surface and a reflection surface for polarized light are aligned and a selective phase film in which xcex/2 phase layers are regularly formed. By employing such a polarized light conversion element, polarized light conversion can be performed with a small space and without extending the width of the light beam emitted from the light source.
In this case, it is preferable that a light-shielding plate array for preventing the intermediate light beams from directly entering the portions of the reflection surfaces be placed on the incident side of the polarized light separation unit array. If such a light-shielding plate array is placed, a degree of polarization of the polarized light beams emitted from the second optical element can be further increased.
In the above first to fourth projectors, it is preferable that the one type of polarized light beams emitted from the second optical element be p-polarized light beams with respect to the polarized light beam selection element. With this construction, a projected image having high contrast can be easily obtained.
In the above first to fourth projectors, a polarizer may preferably be provided on an optical path between the polarized light beam selection element and the projection optical system. With this construction, a degree of polarization of the polarized light emitted from the polarized light beam selection element. Accordingly, an image projected on a display plane or a projection plane via the projection optical system can be increased. Therefore, by placing the polarizer in this way, the contrast of the projected image can be increased, and the extreme high-quality projected image can be obtained.